1. Field of the Invention
The present invention relates to a fuel control system for an engine, and, more particularly, to a fuel control system for an automobile internal combustion engine designed to improve fuel consumption by stopping the supply of fuel when the engine is decelerating.
2. Description of Related Art
Known fuel control systems for internal combustion engines which stop the supply of fuel during deceleration are characterized by a hysteresis region of rotational speeds of engine in which the supply of fuel to the engine is cut off during deceleration, such that the fuel control system cuts off the supply of fuel until the engine decreases its rotational speed below the lower limit of the hysteresis region, and also cuts off the supply of fuel when the engine increases its rotational speed above the upper limit of the hysteresis region. Such a fuel control system is known from, for example, Japanese Unexamined Patent Publication No. 59-5839.
In order for, in particular, automotive vehicles equipped with automatic transmissions, to ensure the prevention of hunting between the supply of fuel and the cut-off of fuel, the fuel control system is characterized by a wide hysteresis region of rotational speeds. This is because an engine of this kind is connected to the associated automatic transmission via a torque converter resulting in considerable changes in rotational speed.
With such a conventional fuel control system, when the rotational speed of engine has dropped below the lower limit of the hysteresis region, the cut-off of fuel is not resumed again until the rotational speed of engine rises above the upper limit of hysteresis region. Therefore, for example, even if the engine is decelerated during supplying of fuel to the engine in the hysteresis region of engine rotational speeds, if the engine does not experience much of an increase in rotational speed while the vehicle is running at a very low speed, the cut-off of fuel does not occur, and this results in an unsatisfactory increase in fuel efficiency.